IS-IS multitopology support

IS-IS multitopology support for IPv6 is a feature that allows the protocol to operate using both IPv4 and IPv6 simultaneously. It removes some restrictions that did not allow this using conventional IS-IS. Specifically, Cisco describes it in its documentation like so:

IS-IS multitopology support for IPv6 allows IS-IS to maintain a set of independent topologies within a single area or domain. This mode removes the restriction that all interfaces on which IS-IS is configured must support the identical set of network address families. It also removes the restriction that all routers in the IS-IS area (for Level 1 routing) or domain (for Level 2 routing) must support the identical set of network layer address families. Because multiple SPFs are performed, one for each configured topology, it is sufficient that connectivity exists among a subset of the routers in the area or domain for a given network address family to be routable.

Links:

https://forum.networklessons.com/t/is-is-route-leaking/1796/21?u=lagapides

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/xe-16/irs-xe-16-book/ip6-route-mult-isis-xe.html#GUID-7067667F-6937-4CD2-ADDA-046DFE0406E6